The invention relates to marine propellers, particularly to marine propellers having a plurality of replaceable blade sections.
Although a variety of replaceable blade propeller assemblies have been proposed, including those shown in U.S. Pat. Nos. 3,764,228, 3,073,395 and 1,010,929, such multiple piece propeller assemblies have not found widespread acceptance, and single piece propellers are presently used on the vast majority of boats. Use of single piece propellers continues despite the numerous advantages that a practical, reliable, low cost piece propeller assembly with replaceable blade sections would have. For example, one piece propellers usually have to be replaced if they strike heavy, solid objects that severely bend one blade of the propeller during operation of the boat. One piece hub and propeller assemblies are very bulky, and require a large amount of storage space in a boat. Furthermore, propeller blades of different pitches are preferable for various types of boat operation. Therefore, it would be advantages for a boat owner to be able to easily and conveniently change blade pitches for different types of operation, such as pulling skiers or high speed cruising. Many single piece propeller assemblies include through-the-propeller exhaust systems having a plurality of passages in the central portions of the hub through which exhaust gases can escape without interferring with flow of water around the propeller blades during normal boat operation. U.S. Pat. No. 3,876,331 discloses a three-piece marine propeller assembly having removable blade sections and exhaust gas passages through the hub portion thereof. However, none of the three-piece replaceable blade propeller assemblies mentioned above have found wide-spread acceptance because of their complexity. All of them have been implemented by means of inherently flimsy mortise and tenon or collar arrangements for connecting the opposed flanges of the blade support sections to a main hub. Besides being inherently rather flimsy, the proposed devices have been unduly expensive because the main components have been required to be precisely machined to a great extent to provide close tolerance required by the type of construction required by the design of the prior replaceable blade propeller assemblies.
Despite the variety of proposed replaceable blade propeller assemblies that have been introduced, there remains a need for a low cost, highly reliable, easily replaceable multiple piece replaceable blade propeller assembly that is substantially more satisfactory to the boating public than in the device yet proposed.
Accordingly, it is an object of this invention to provide a low cost, highly durable, easily installable replaceable blade marine propeller system that is significantly less complex in design than those of the above-mentioned prior art.
Many commonly used marine propellers utilize rubber shock absorption devices in their hub assemblies to reduce shock transmitted from a propeller blade that strikes an obstacle to the drive train or motor of the boat to reduce damage thereto. Provision of such rubber shock absorbing devices adds to the complexity of its construction and expense of marine propellers, especially those having through-the-propeller exhaust passages, which are highly desirable in order to achieve efficient propeller operation and avoid cavitation under high performance operating conditions.
FIG. 8 illustrates such a prior art device, which can typically be a propeller manufactured by Mercury and other companies. Reference numeral 69 designates one of the above-mentioned rubber shock absorption devices, and consists of a rubber or other resilient cylindrical sleeve that is very tightly pressed (displacing at least a quarter of an inch of rubber) into hole 70 of the hub 71 of marine propeller 72. The rubber sleeve is thermally bonded onto the outer cylindrical surface of an adaptor 74, which is usually composed of brass or steel. Adaptor 74 has an axial cylindrical hole 75 therein with a plurality of horizontal keyways disposed in its wall for receiving the respective splines 76 of the drive shaft 77 of a marine motor.
Typically a hydraulic press is used to apply a great deal of pressure to force the shock mount 69 into hub hole 70. This type of shock mount has a number of disadvantages, the main one being that sometimes a "hot bonded" interface between the rubber sleeve and the spline driver breaks under stress. The propeller then must be repaired, and this repair must be done in a shop with proper equipment, and cannot possibly be done by the owner of a pleasure boat. If the owner did not have a spare propeller, he would have to "limp" back to a landing site and discontinue his boating activity until a spare propeller could be obtained. Furthermore, occasionally when a propeller driven by a large, high powered marine engine strikes a large rock or the like, the above-mentioned prior art rubber shock mounts do not sufficiently isolate the drive train from the resulting shock. Consequently, expensive out-drive mechanisms and marine motors are sometimes damaged.
Accordingly, it is another object of the invention to provide a shock mount coupling means between a drive shaft and a hub, which shock mount coupling means can be easily and inexpensively repaired or replaced without use of specialized equipment such as a hydraulic press or device for bonding a resilient sleeve to a splined driver.
It is another object of the invention to provide a means for shock mount coupling a marine propeller hub to a drive shaft to isolate a drive train connected to the hub from shock imparted to the propeller more effectively than prior art shock mount coupling devices.